Without knowing what version of OpenBSD is installed, all anyone will be able to suggest is to install a recent snapshot of -current & see if problems persist.

Note that suspend/resume functionality radically changed in the OpenBSD 4.8-release timeframe & post-4.8-release timeframe. Snapshots of -current are now beyond what will officially be released as OpenBSD 4.9-release in May 2011. A lot of code has changed in the last nine months. This may or may not have solved your problem, but what the project developers will be most interested in (if there is a need to get them involved...) is how the current code base behaves.

A number of suspend/resume issues were solved after OpenBSD 4.8 was cut. Unless you want to wait for the release of OpenBSD 4.9-release. it would still be good to install a snapshot of -current to gauge whether any of problems with your hardware have been solved there.

As mentioned before, snapshots of -current already incorporate newer code than what will be found in the official OpenBSD 4.9-release.

I had some free spare time and I tried the 4.9 snapshot. Good news the laptop can suspend/resume but under a text console only. When I am under a window manager or going from a resumed console (eg tty1) to a window manager the system seems to hangs (I see some vertical white stripes on the bottom half of the screen).
I can see the same vertical stripes (very quick) when I reset the window manager (control-alt-backspace) under normal conditions , so I assume the gfx card cannot be initialized properly after resume..?

Kernel recognition for your video card, an NVIDIA GeForce 8400M GS, was added to OpenBSD 6 October 2008. That addition to the kernel is entirely separate from system suspend/resume issues.

ACPI is a standard that is .... very, very, VERY loosely observed by hardware integrators. And NVIDIA was a known issue last year during the revamp of suspend/resume. Quoting Theo De Raadt, OpenBSD Founder, 6 August 2010: (Ref: http://marc.info/?l=openbsd-tech&m=128106745707385&w=2)

"We will continue to have problems with....Nvidia video. I think we don't stand a chance of ever doing this. Don't buy Nvidia."

You have a functioning laptop with suspend/resume if you transition to a text console first. Consider yourself lucky. FreeBSD users do not have suspend/resume with your 1400.